There are known hydrogen separation membranes for separating hydrogen from a hydrogen-containing gas by selective permeation. Materials for forming a hydrogen separation membrane include various materials such as various metals, alloys, and ceramics and molecular sieve carbon, a typical example of which is Pd-based alloys (Patent Document 1). A hydrogen separation membrane formed of Pd-based alloy, however, shows only two to three times higher hydrogen separation performance even if a rare earth element, such as Y or Gd, having a great performance-improving effect is added and also has a disadvantage of high cost because Pd itself is a precious metal.
As an alternative to Pd-based alloy membranes, Patent Document 2 discloses a Nb-based-alloy hydrogen separation membrane mainly containing Nb and alloyed with one or more elements selected from the group consisting of V, Ta, Ni, Ti, Mo, and Zr. Patent Document 3 discloses, as a hydrogen separation membrane formed of a Nb alloy, a hydrogen separation membrane formed of a Nb alloy containing 5% to 25% by mass of at least one element selected from the group consisting of Pd, Ru, Re, Pt, Au, and Rh. Patent Document 4 discloses that a Nb foil covered with a Pd membrane on each side has the largest amount of hydrogen permeated as compared with Ta and V foils similarly covered with a Pd membrane on each side.
Patent Document 2 discloses a Nb-based-alloy hydrogen separation membrane formed of an alloy of Nb with one or more of the six elements including V, Ta, Ni, Ti, Mo, and Zr, and Patent Document 3 discloses a hydrogen separation membrane formed of an alloy of Nb with one or more of the six elements including Pd, Ru, Re, Pt, Au, and Rh, although they do not disclose that an alloy membrane of Nb and W or an alloy membrane of Nb, W, and Ta is effective as a hydrogen separation membrane.
Patent Document 1: U.S. Pat. No. 2,773,561
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2000-159503
Patent Document 3: Japanese Unexamined Patent Application Publication No. 2002-206135
Patent Document 4: U.S. Pat. No. 3,350,846